Firefox 57 (Quantum) for developers

This article provides information about the changes in Firefox 57 (a.k.a. Firefox Quantum) that will affect developers. Firefox 57 was released on November 14, 2017.

Firefox 57 === Firefox Quantum

Firefox 57 has been given the release name Quantum, after the Firefox Quantum engineering project that has aimed to rebuild Firefox from the ground up, bringing with it major performance, stability, and visual improvements. This is the first version of Firefox to ship some of these improvements, so we wanted to mark the occasion.

Firefox's new parallel CSS engine — also known as Quantum CSS or Stylo — is enabled by default in Firefox 57 for desktop, with Mobile versions of Firefox to follow later on. Developers shouldn't notice anything significantly different, aside from a whole host of performance improvements. There are however a number of minor functional differences in Stylo, implemented to fix non-standard Gecko behavior that should be eliminated. We will report on such differences on reference pages and in the release notes as appropriate (see Quantum CSS notes).

The layout.css.clip-path-shapes.enabled preference has been removed (bug 1399767). This preference allowed disabling the <basic-shape> support in clip-path. This support was shipped in Firefox 54 and can no longer be disabled.

Quantum CSS notes

Following bugs have been fixed in Quantum:

Radial gradient values like radial-gradient(circle gold,red) will work in the old Gecko style system, even though they shouldn't because of the missing comma between circle and gold (bug 1383323).

When you animate an offscreen element onscreen but specify a delay, Gecko does not repaint on some platforms, e.g. Windows (bug 1383239).

In Gecko, cancelling a filling animation (e.g. with animation-fill-mode: forwards set) can trigger a transition set on the same element, although only once (see bug 1192592 and these test cases for more information). In general declarative animations should not trigger transitions.

Animations using em units are not affected by changes to the font-size on the animated element's parent in Gecko, whereas they should be (bug 1254424).

Gecko also deals with font-size inheritance differently from Quantum CSS, meaning that for some language settings inherited font sizes end up being smaller than expected (see bug 1391341).

Gecko reuses the same mechanism used when parsing a url-token when parsing the domain() or url-prefix() URL matching functions for a @-moz-document rule. Quantum CSS does not use the same mechanism and it does not consider tokens invalid when they contain brackets or quotes (bug 1362333).

In Gecko, when you set a system font as the value of a canvas 2D context's font (e.g. menu), getting the font value fails to return the expected font (it returns nothing). This has been fixed in Quantum. (bug 1374885).

In Gecko, when you create a detached subtree (e.g. a <div> created using createElement() that is not yet inserted into the DOM), the subtree's root element is set as a block-level element. In Quantum CSS this is set as inline, as per spec (bug 1374994).

Because Firefox doesn't yet support the SCTP ndata protocol that provides the ability to interleave SCTP messages from multiple sources, sending large data objects can cause significant delays on all other SCTP traffic. See bug 1381145 to track progress on implementing and deploying ndata support in Firefox..

The RTCDataChannel.send() method can now throw a TypeError exception if the size of the message you're trying to send is not compatible with the receiving user agent (this is implemented as part of bug 979417).

Security

Data URIs are now treated as unique opaque origins, rather than inheriting the origin of the settings object responsible for the navigation (bug 1324406).

Plugins

No changes.

Other

Firefox headless mode now includes a -screenshot flag that allows you to take website screenshots directly from the command line (bug 1378010).

Removals from the web platform

HTML

<link rel="preload"> (see Preloading content with rel="preload") has been disabled in Firefox 57 because of various web compatibility issues (e.g. bug 1405761). An improved version that works for non-cacheable resources is expected to land in Firefox 58.